Factor b and c2 protein point mutants, a method for enhancing the activity of anti-cancer antibodies, the pharmaceutical composition and the use of mutants

ABSTRACT

The subject of this invention is point mutants of human proteins constituting the complement system&#39;s C3 and C5 convertases, where the mutation are as follows: For the factor B:—D279G, F286L, K323E, Y363A; D279G_F286L_K323E_Y363A-quadruple mutant; For the C2 protein:—C261A, Q.263G, Y347A, L348A; T442Q, double mutants C261A_Q263G and Y347A_Q263G, triple mutant Y347A_Q263G_T442Q The subject of this invention is the method of enhancing the activity of the anti-cancer antibodies, which includes the addition of mutants defined above. The subject of this invention is the pharmaceutical composition, which includes the therapeutically effective number of mutants defined above. The subject of this invention is the use of mutants defined above to enhance the cytotoxic activity of anti-cancer antibodies in therapy and in the treatment of neoplastic diseases.

The subject of the invention are the point mutants of human proteins being part of complement system's C3 and C5 convertases, specifically factor B and C2 protein. Moreover, it is an anti-cancer antibodies effectiveness enhancing method, which includes adding mutants specified above. The subject of the invention is a pharmaceutical composition that includes a therapeutically effective mutant amount and the use of mutants in enhancing the cytotoxic activity of the anti-cancer antibodies in therapy and in the treatment on neoplastic diseases.

The introduction of cancer cell determinants recognizing antibodies to a standard cancer therapy has contributed to a significant prolonging of the patient survival time and to a reduction in the tumor progression rate. The rituximab recognizing the CD20 molecule, used in leukemia and lymphoma treatment is a prototype of the therapeutic anti-cancer antibody.

Rituximab, and a set of other antibodies approved for clinical use, kills cancer cells in cooperation with human immune system. The binding of the antibody to the surface of a cancer cell activates the complement system—an enzymatic cascade located in the blood serum, whose elements, as a result of the activation, is inserted into the cell membrane of the target cell. The final effect of the complement system activation is a formation of pores and an osmotic lysis of the target cell. Additionally, the complement components' coating of the cancer cell facilitates its absorption by other cells of the immune system by means of phagocytosis.

Although the anti-cancer antibodies have revolutionized the treatment, clinical response does not concern all of the patients, moreover, a resistance to the therapy occurs in some cases. One of the reasons for resistance to the therapeutics operating through the complement system is the overexpression of complement system inhibitors on the cancer cell surface and a depletion of the complement proteins pool through the system activation by the antibodies, which results in insufficient complement activity during subsequent drug administrations.

The description of US2011059072 A invention discloses the method of obtaining and selecting monoclonal antibodies by means of the ADCC type test, which are capable of activating the type III Fcy receptors and have a particular glycan structure.

The description of US2008003646 A invention discloses improved antibodies against tumor surface antigens and their use in cancer treatment. Particularly interesting are the highly stable, humanized antibodies with a high affinity to the carcinoembryonic antigen (CEA), specifically the sm3E antibody, that is derived from the scFv MFE-23 antibody. Such antibody modifications can potentially improve the therapeutic efficacy.

The invention being the subject of this description suggests a solution in the form of anticancer antibodies supplementation with mutant human proteins being a part of the enzymatic complexes (convertases) responsible for the C3 and C5 complement protein proteolysis to their C3b and C5b active fragments. Factor B building convertases of the alternative pathway of the complement system, as well as C2 protein which plays an analogous role in the classical pathway of the complement system, are examples of such proteins. Suitable mutations of the abovementioned proteins are the ones that affect convertases interaction with their inhibitors, by which both activity and the half-life of the enzyme complex alike is greatly extended and the production of the C3b and C5b fragments optimal for the cytotoxic effect is ensured.

The C2 and factor B mutants added in the in vitro test on a CD20-positive lymphoma cells to the human serum and a specific anti-CD20 antibody caused a complete lysis of the cells moderately sensitive to anti-CD20 antibodies. Additionally, the C2 protein mutants caused a statistically significant increase in the death rate of the cells weakly sensitive to anti-CD20 antibodies. Importantly, the increase in the cytotoxic effect, both in the moderately and weakly sensitive to anti-CD20 antibodies lines, was not possible to obtain through increasing the anti-CD20 antibodies concentration without the addition of the mutant proteins (FIG. 1).

In other words, supplementation with appropriately mutated C2 proteins and the factor B increases the cytotoxic activity of the anti-cancer antibodies working through the complement system and simultaneously replenishes the pool of the used complement system components needed to sustain the cytotoxic potential of the human serum.

Point mutations ensuring the insensitivity of the complement system's convertases to the endogenous inhibitors (the so called gain of function mutations), such as CD55, CD46, CD35, factor H, and resulting in an increased activity of the convertases, have been known to the researchers of the autoimmune phenomena. Mutations of this type located in the factor B were defined as an etiological factor of diseases such as C3 glomerulopathy and an atypical haemolytic-uraemic syndrome and in the international literature were univocally associated with pathological phenomena.

The novelty of the proposed solution consists in the use of such potentially pathogenic proteins as an immunotherapy supplement significantly increasing the cytotoxic activity of the immunotherapeutics.

Inhibition of the convertases is one of the main refractory mechanisms of the cancer cells to the complement-based therapies. Studies on model prevention of cancer resistance mechanisms include silencing the complement inhibitor's expression by a siRNA constructs transfection, or the use of bispecific antibodies that recognize the cancer cells' antigen determinant and simultaneously block the complement inhibitor (e.g. CD55).

A disadvantage and a practical limitation of the first solution is the necessity of a precise delivery of siRNA constructs to the cancer cells due to the widespread expression of the complement inhibitors in the human body. The latter of the mentioned approaches is limited to simultaneous inhibition of only one complement inhibitor, determined by the specificity of the antibody, while the cancer cells are producing or capturing several types of inhibitors from the environment.

Gain of function mutants ensure insensitivity of the complement convertases to more than one inhibitor type, and additionally, a creation of a multiple mutant which groups phenotypic characteristic of several single gain of function mutants is possible, which has been proven in the hereby in vitro studies. The activity of a multiple mutant exceeds the cytotoxicity enhancing activity of immunotherapeutics of single mutants. Moreover, a protein constructed that way is more versatile in relation to cancer cells displaying different patterns of complement inhibitor expression. A noticeable increase in the cytotoxic activity of the in vitro antibodies has been observed by supplementation of the factor B with a multiple gain of function mutations, at a concentration corresponding to 25% physiological concentration of this protein in the serum (FIG. 2).

C2 is an element of the classical pathway, which is not activated spontaneously as in the alternative pathway (which consists of the factor B), but in response to the appearance of a specific stimulant, e.g. anti-cancer antibodies deposited onto the surface of the target cell. In other words, the process of the classical convertases formation with the participation of the mutated C2 protein may be controlled by coordinating its administration with the administration of immunotherapeutics. In contrast to the factor B, there's currently no known naturally occurring gain of function type C2 mutation (or any other protein typical for the classical complement pathway), that has been identified as a cause of autoimmune disorders. Another benefit of the use of hyperactive C2 protein mutants is the C2's physiological concentration in the serum of only 25 μg/ml, which would require a significantly smaller amount of the recombinant C2 protein for effective supplementation than in the case of factor B supplementation (physiological concentration 180 μg/ml).

Considering that the naturally occurring gain of function type mutants are unknown, but the C2 and the factor B proteins exhibit a significant degree of homology between them, C2 mutants have been created, that correspond to the sequence of mutated, hyperactive factor B variants. Single and multiple gain of function C2 protein mutants showed an analogical to the mutated factor B, significant increase in the cytotoxic activity of the anti-CD20 antibodies (FIG. 3).

The creators of this invention postulate the supplementation with such mutants, with the use of the method of counteracting the cancer cells resistance to immunotherapeutics caused by the overexpression of complement inhibitors.

The mutants can be administered as a supplement, or in a pharmaceutically acceptable form, along with antibodies authorized for clinical use in an anticancer therapy. In such pharmaceutical and therapeutic compositions, the mutants are beneficially used along with one, or more, pharmaceutically authorized carriers and optionally with other therapeutic components. The carriers have to be pharmaceutically authorized in the sense that they remain compatible with other components of the composition and are not excessively harmful to the recipient. The mutants are administered in amounts effective for achieving the desired pharmacological effect, as described above/in the examples. The compositions include those that are suitable for both parenteral and non-parenteral administration, specific ways of administration include also intravenous administration.

The objective of this invention is to providing the supplementation of accordingly mutated C2 proteins and/or factor B, which enhances the cytotoxic activity of the anti-cancer antibodies and could be used for standard anti-cancer therapy with antibodies.

The essence of the invention in question is point mutants of human proteins that make up the complement system's C3 and C5 convertases, where the individual mutations are:

-   -   For the factor B:—D279G, F286L, K323E, Y363A;         D279G_F286L_K323E_Y363A-quadruple mutant;     -   For the C2 protein:—C261A, Q263G, Y347A, L348A; T442Q, double         mutants C261A_Q263G and Y347A_Q263G, triple mutant         Y347A_Q263G_T442Q

Mutants which enhance the cytotoxic activity of the anti-cancer antibodies acting with the participation of the complement system.

A method of enhancing the anti-cancer antibodies activity, which includes adding the mutants mentioned above.

A pharmaceutical composition, which includes the therapeutically effective amount of the mutants mentioned above.

The use of the above-mentioned mutants to enhance the cytotoxic activity of the anti-cancer antibodies in the therapy.

The use of the above-mentioned mutants to enhance the cytotoxic activity of the antibodies in the treatment of neoplastic diseases.

The use of the above-mentioned mutants to enhance the cytotoxic activity of the serum in patients undergoing immunotherapy.

The terms used above, in the description and in the patent claims, have the following meaning: Gain of function type mutants—mutants in the proteins that build the alternative and classical convertases of the complement system, which result in an increased activity of the convertases and/or their longer half-life. Convertases—an enzyme complex formed during the complement cascade's activation, built from C3 protein and factor B fragments, C3bBb (alternative C3 convertase), C3bBbC3b (alternative C5 convertase) or C2, C4 and C3 protein fragments, respectively C4b2a (classical C3 convertase) and C4b2aC3b (classical C5 convertase) respectively. Supplementation—complementing the antibodies-based anti-cancer therapy (anti-cancer antibodies recognize the antigen determinants of the cancer cells). The supporting factor/supplement is identical with supplementation. Complement system—a group of proteins present in the blood serum, creating an enzymatic-proteolytic cascade resulting in the formation of a membrane attacking complex. The description of the complement system and its individual proteins can be found in the literature such as “The Complement FactsBook” edited by Scott Barnum Theresa Schein, ed. 2, 2017, Academic Press.

FIGURES Description of Figures

FIG. 1—demonstrates the cytotoxic effect of anti-CD20 antibodies depending on the dose of antibodies.

FIG. 2 shows the cytotoxic effect of anti-CD20 antibodies after serum supplementation with recombinant gain-of-factor B factor mutations. The NHS (normal human serum) symbol was used for the serum without the addition of factor B, the WT (wild-type) symbol for the result of wild type (non-mutated) type supplementation and to the height of this bar (dashed line) reference to the calculations of statistically significant differences were made. Factor B mutants markings refer to the position of a given amino acid in the native protein (the numbering includes the signal sequence) and changes of a specific amino acid naturally occurring in a given position (letter before the amino acid position number expressed with the so-called one-letter code) to the amino acid resulting from the mutation (letter after position number expressed using the so-called single-letter code). The 4× marking corresponds to a quadruple mutant grouping the mutations D279G, F286L, K323E and Y363A. The ANOVA test with Dunnett post-test showed statistical significance for supplementation with the factor B quadruple gain of function mutation in the case of Raji cells at the significance level of p<0.05 (*).

FIG. 3A—shows the anti-CD20 antibodies cytotoxic effect after the serum supplementation (at the concentration optimal for visualizing the antibodies' cytotoxic effect in a given cell line −10% for the Raji cells and 20% for Namalwa cells, respectively) with C2 protein's gain of function recombinant mutants. Markings on the graph analogically to FIG. 2. The statistical significance according to the ANOVA test with Dunnett post-test at a level of p<0.001 is marked on the chart with a *** symbol and the significance at a level of p<0.05 with a * symbol.

FIG. 3B—shows overall experiment results comprising two lower, suboptimal serum concentrations for which the cytotoxic effect of the anti-CD20 antibodies in a given cell line was tested.

FIG. 4 shows results of an additional experiment that compared the effect of single mutants ((Y347A, Q263G, T442Q), double mutant (Q263G_Y347A) and a triple mutant (Q263G_Y347A_T442Q)) on the Namalwa cells in an optimal serum concentration (20%, FIG. 4A) and additionally with two suboptimal serum concentrations (FIG. 4B). The markings on the charts accordingly to FIG. 2 and FIG. 3. The statistical significance according to the ANOVA test with a Dunnett post-test at a level of p<0.001 is marked on the chart with a *** symbol, and the significance at a level of p<0.05 with a ** symbol.

FIG. 5 shows results of an experiment in which the effect of C2 protein supplementation of the serum taken from patients treated with rituximab anti-CD20 antibody combined with an additional amount of another anti-CD20 antibody ofatumumab was tested. The effect of supplementation with the use of the recombined wild-type C2 protein (WT) and supplementation of the C2 protein multiple mutant (Q263G_Y347A_T442Q) were compared. The experiment was carried out with a 50% patient serum concentration (which reflected the physiological conditions) on the Namalwa cell line characterized by a low level of sensitivity to anti-CD20 antibodies. The ANOVA test with a Dunnett post-test showed a statistical significance to the multiple C2 protein gain of function mutant's supplementation in relation to a supplementation with unmutated (WT) protein at a significance level of p<0.01 (**).

FIG. 6 shows results of an experiment in which the 50% serum taken from patients after the rituximab administration (and thus containing some amount of rituximab unused by the immune system) was supplemented with a C2 protein multiple mutant (Q263G_Y347A_T442Q) or an unmutated protein (WT) and then was used in a cytotoxic test on Raji cells. The ANOVA test with a Dunnett post-test showed a statistical significance for supplementation with the multiple C2 protein gain of function mutant (causing a complete lysis of the Raji cells by the patients' sera) in relation to the supplementation of unmutated protein (WT) at a significance level of p<0.001 (***).

Seq.1—means a factor B's sequence with a signal sequence (single-letter amino acid code).

Seq.2—means a C2 protein's sequence with a signal sequence (single-letter amino acid code).

The invention is illustrated by, but not limited to, the following examples:

EXAMPLE 1 Description of Methodology

The cDNA reference sequences of the C2 proteins (accession number NM_000063.5) and the factor B (accession number NM_001710), additionally containing at the end 3′ triplets for six histidine residues, have been optimized in terms of the GC pairs content, the presence of unfavorable secondary structures and the so-called rare codons through the ThermoFisher Scientific algorithm. The optimized sequences were then synthesized de novo and cloned to the pCEP4 expression plasmid. The constructs were once again verified with the help of the DNA sequencing. Plasmids verified for the sequence correctness were transformed into the DH5a strain E. coli bacteria, from which the plasmid DNA was purified with the help of MidiPrep Kit (Qiagen) in the amount necessary for the eukaryotic cells' transfection. With the help of 30 μg of plasmid DNA and the Freestyle Max (ThermoFisher) reagent, a transfection of the HEK 293 Freestyle cells was performed. The cells were grown for 7 days in the Freestyle 293 Expression Medium (ThermoFisher), while the growth medium was harvested on the second, fourth and seventh day after the transfection and resupplied with a fresh medium. The harvested, cell-conditioned medium was stored at −80 C until the protein purification process with the use of affinity chromatography. For this purpose, HisTrap FF crude (GE Healthcare) columns were used. Washing and balancing the columns were performed in a 20 mM Tris-HCl pH 8.0 buffer with addition of 1 mM of imidazole. The elution was conducted with the use of 0.7 M imidazole in the same buffer. The protein containing eluate fractions were merged, dialyzed on the PBS buffer and concentrated with the use of Vivaspin mwco. 10 kDa (Millipore) concentrator. On the basis of the cDNA optimized matrix, the cDNAs of factor B's single mutants D279G, F286L, K323E, Y363A were created and the multiple mutant containing all of the substitutes mentioned above (4×), whereby the protein expression of single F286L mutant was not achieved. Similarly, complement C2 protein single mutants (R243C, C261A, Q263G, S307E, Y347A, L348A, T442Q) were created successively as well as double mutants C261A_Q263G and Y347A_Q263G and the triple mutant Y347A_Q263G_T442Q.

The human Raji and Namalwa lymphoma cells expressing the CD20 marker on their surface were used for experiments. The Raji cells incubated in the presence of human serum are characterized by an average sensitivity to anti-CD20 antibodies, the maximum achievable level of cells' lysis oscillates within 50%. The Namalwa cells are characterized by a low sensitivity to the anti-CD20 antibodies due to the less favourable ratio of the CD20 molecules to the amount of the complement system's surface inhibitors, such as CD46, CD55 and CD59. Depending on the experiment, the Namalwa cells' lysis level in the presence of the serum and the anti-CD20 antibodies oscillated between 10 and 20%. The impact of the recombined factor B and the complement system's C2 protein on the anti-cancer activity of the anti-CD20 antibodies was tested in an in vitro cytotoxic test. Cells suspended in the RPMI medium with a 10% bovine serum addition were incubated with a 1 mM calcein derivative (calcein-AM), which is actively collected by living cells and metabolized to a fluorescent derivative. The incubation was carried out at 37° C. in a 5% CO2 environment for 30 minutes. The cells were then washed three times with a PBS buffer, suspended in a PBS buffer supplemented with a 1 mM CaCl₂ and MgCl₂ and added in the amount of 100.000 to the well of a V-shaped multi-well plate. After centrifugation and supernatant's removal, the cell pellet was suspended in human serum with anti-CD20 antibody (ofatumumab) in a standard concentration of 50 μg/ml. For the Raji cells 10% serum was used as a concentration for optimal visualization of the anti-CD20 antibodies cytotoxic effect, for the Namalwa cells analogically the concentration was increased to 20%. Additionally, in selected experiments 50% serum collected from patients suffering from B cell-derived tumors treated with rituximab therapeutic anti-cancer antibody was used. The final reaction volume was 50 μl. The cells were incubated with the serum and with anti-CD20 antibodies for 30 minutes in a thermomixer (Eppendorf) at 37° C. and with shaking at 650 rpm. After the incubation was finished another 50 μl of the PBS buffer was added and then the plate with the cells was centrifuged at a speed of 1000×G for 2 minutes. 80 μl of the supernatant was moved to the wells of a 96-well flat-bottomed plate and the fluorescence of the collected supernatants was measured at excitation/emission wavelengths of 485 and 515 nm, respectively. The intensity of the fluorescence was directly proportional to the fluorescence of the derivative released from the cells due to the lysis induced by the complement system contained in the serum. The cells incubated with the heat-inactivated serum (56° C., 30 min) and thus lacking the complement's activity were treated as a negative control, i.e. a lysis independent of the complement system's activity.

In the first experiment it was shown that the increase in the dose of the anti-CD20 antibodies at a constant serum concentration does not significantly increase the percentage of the cells destroyed. (FIG. 1)

The bar marked with a Δ 500 symbol illustrated the effect of the maximum antibody concentration (500 μg/ml) and a heat-inactivated serum. Its height illustrates the level of lysis of cancer cells independent from the complement system. The ANOVA test with a Dunnett post-test did not show statistically significant differences between the 50 μg/ml concentration and the higher concentrations.

In contrast to increasing the antibodies' concentration, increasing the cytotoxic effect was possible after the serum (NHS) supplementation with factor B gain of function type mutants (FIG. 2) and analogical complement's C2 protein mutants (FIG. 3). The concentration of the used mutants was equal to the physiological concentration of the proteins in the serum at a given concentration. For a 10% serum they were 2.5 μg/ml C2 and 20 μg/ml factor B and 5 μg/ml C2 protein for a 20% serum.

In the case of C2 protein, a panel of single gain of function mutants, two double mutants and one triple mutant, were made. The best effects (statistically significant increase in the cell's lysis percentage) in experiments performed in the Raji cells with single and double mutants were obtained for a Y347A_Q263G mutant-ANOVA test with a Dunnett post-test showed significance at a level of p<0.001 in the Raji cells case. A single Y347A mutant was at a similar level. It should be noted however, that a noticeable effect of the Y347A_Q263G double mutant increasing the cytotoxicity of the anti-CD20 antibodies was already present at a suboptimal 5% serum concentration (FIG. 3B). In the case of Namalwa cells, statistically significant differences in the wild-type C2 protein supplementation were found in Q263G, T442Q, Y347A, C261A_Q263G, Y347A_Q263G and Y347A_Q263G_T442Q mutants (separate experiment depicted in FIG. 4). The R243C mutant was treated as a negative control due to the mutation's characteristic disrupting the structure, and hence, the function of the C2 protein. Double mutants, whose efficacy on the Namalwa line was demonstrated at a 20% serum's concentration noticeably increased the cytotoxic effect also in a suboptimal 10% serum's concentration (FIG. 3B). The obtained results suggest, that the multiple mutants work more efficiently under conditions of other complement proteins' deficiency, which can reflect an in vivo situation, in which the complement's pool is depleted due to earlier immunotherapy rounds or a primary or secondary immunodeficiency.

In a separate experiment on Namalwa cells the anti-CD20 antibodies' cytotoxic effect with supplementation with single (Y347A, Q263G, T442Q), double (Q263G_Y347A) and triple (Q263G_Y347A_T442Q) C2 protein mutants was compared (FIG. 4). The aim of the experiment was to show, that the accumulation of single C2 protein gain of function type mutations in one protein construct does not lead to the loss of C2 protein activity but may cause an additive effect manifested by both a higher antibodies' cytotoxicity at an optimal serum concentration and a significantly higher percentage of killed cells at a suboptimal serum concentration, in comparison to the results obtained under analogical conditions for single mutants. Such actions are desirable from a practical point of view because it ensures a much more beneficial supplementation effect.

In the next experiment the Namalwa line cells along with sera (in the final 50% concentration corresponding to the physiological conditions) taken from the patients with B cell-derived tumors treated with rituximab were used. Serum samples were taken from patients directly before and directly after the administration of rituximab. The rituximab's administration causes a mass activation of the complement system in this type of patients, which in turn is manifested by a decreased serum's cytotoxic activity after the drug administration, due to the consumption of the complement protein pool. A sustained state of decreased cytotoxic activity may cause a decreased rituximab's efficacy in relation to cancer cells that have not been killed during the first administration of the drug. The sera were first supplemented with another anti-CD20 antibody, analogical to rituximab: ofatumumab. Next, the sera were supplemented with a recombinant wild type C2 protein and Q263G_Y347A_T442Q multiple C2 protein mutant at a concentration of 12.5 μg/ml. The cytotoxic test results showed that supplementing the patients' sera with a multiple mutant can not only increase the cytotoxic effect of the patient before the drug administration but can also counteract the reduction of the cytotoxic activity of patients' sera following the rituximab's administration at the time when the drug's activity is leading to exhaustion of the complement system's protein pool (FIG. 5). The described multiple mutant's effect could not be obtained by a supplementation with a recombinant, wild type (WT) C2 protein variant.

An analogical experiment, in which the effects of the wild type (WT) and triple mutated (Q263G_Y347A_T442Q) C2 protein supplementation on the cytotoxic potential of the sera collected from the same patients as in FIG. 5, although without the addition of saturating concentration of ofatumumab, was carried out on the Raji cell line (FIG. 6). In this experimental setup, the only present anti-cancer drug was the excess rituximab remaining after the intravenous administration, which was not used by the immune system to the cancer cell elimination. The addition of 12.5 μg/ml of a triple mutated C2 protein allowed for a complete lysis of the Raji cells by sera collected from patients after the rituximab's infusion, whereas the result for the sera without the C2 addition or with an addition of a unmutated (WT) C2 protein ranged between 50% and 70% of a complete lysis depending on the patient. The obtained results illustrate the example, when not the bioavailability of the drug, but the decrease in serum's cytotoxic activity is the factor limiting a successful anti-cancer antibody therapy and when the of gain-of-function C2 protein mutants can significantly increase the effectiveness of the drug already present in the patient's bloodstream by strengthening the complement system's activity.

RESULTS SUMMARY

It has been shown, that some gain of function type mutations in the C2 proteins and in the factor B can significantly increase the cytotoxic activity of the anti-CD20 antibodies such as ofatumumab, for example. An analogical supplementation effect is to be expected for other anti-cancer antibodies known from literature (e.g. rituximab, alemtuzumab) acting via the complement system. It has been shown, however, that a similar effect cannot be reproduced by increasing the dose of antibodies alone. An accumulation of many point mutations in one protein may give a cumulative effect, as in the case of a quadruple factor B D279G_F286L_K323E_Y363A mutant or the C2 protein Y347A_Q263G, C261A_Q263G, Y347A_Q263G_T442Q mutants. The use of multiple C2 protein mutants such as Q263G_Y347A_T442Q was able to counteract the decrease in the cytotoxic potential of the sera collected from the patients after the anti-CD20 antibodies administration and also to significantly better utilize the anti-cancer potential of the antibodies remaining the patients' sera after the drug administration. As an element of novelty, we emphasize the use of such mutants as a universal supplement in antibodies anti-cancer immunotherapy.

LITERATURE

-   1. Stasilojc G, Osterborg A, Blom A M, Okroj M. New perspectives on     complement mediated immunotherapy. Cancer Treat Rev 2016; 45:68-75. -   2. Urban A, Borowska A, Felberg A, van den Heuvel L, Stasilojc G,     Volokhina E, et al. Gain of function mutant of complement factor B     K323E mimics pathogenic C3NeF autoantibodies in convertase assays.     Autoimmunity 2018; 51:18-24. -   3. Fishelson Z, Donin N, Zell S, Schultz S, Kirschfink M. Obstacles     to cancer immunotherapy: expression of membrane complement     regulatory proteins (mCRPs) in tumors. Mol Immunol 2003; 40:109-23. -   4. Mamidi S, Hone S, Teufel C, Sellner L, Zenz T, Kirschfink M.     Neutralization of membrane complement regulators improves     complement-dependent effector functions of therapeutic anticancer     antibodies targeting leukemic cells. Oncoimmunology 2015; 4:e979688. -   5. Macor P, Secco E, Mezzaroba N, Zorzet S, Durigutto P, Gaiotto T,     et al. Bispecific antibodies targeting tumor-associated antigens and     neutralizing complement regulators increase the efficacy of     antibody-based immunotherapy in mice. Leukemia 2015; 29:406-14. -   6. Okroj M, Eriksson I, Osterborg A, Blom A M. Killing of CLL and     NHL cells by rituximab and ofatumumab under limited availability of     complement. Med Oncol 2013; 30:759. 

1. Point mutants of human proteins constituting the complement system's C3 and C5 convertases, characterized in that: For factor B:—D279G, F286L, K323E, Y363A; D279G_F286L_K323E_Y363A-quadruple mutant; For C2 protein:—C261A, Q263G, Y347A, L348A; T442Q, double mutants C261A_Q263G and Y347A_Q263G, triple mutant Y347A_Q263G_T442Q
 2. Mutants according to claim 1, characterized in that they enhance the cytotoxic activity of the anti-cancer antibodies working with the complement system's use.
 3. The method of enhancing the anti-cancer antibodies' activity characterized in that it includes the addition of mutants defined in claim
 1. 4. The pharmaceutical composition characterized in that it includes the therapeutically effective number of mutants defined in claim
 1. 5. The use of mutants defined in claim 1 for enhancing the cytotoxic activity of anti-cancer antibodies in therapy.
 6. The use of mutants defined in claim 1 for enhancing the cytotoxic activity of anti-cancer antibodies for the treatment of neoplastic diseases.
 7. The use of mutants defined in claim 1 for enhancing the cytotoxic activity of the serum in patients treated with immunotherapy. 